Due to the progress in the semiconductor technology, integrated circuit (IC) chips have been widely used in various electronic apparatus, such as personal computers, notebook computers and network servers. While the IC chips have significantly increased computing speed and functions, they also generate correspondingly increased waste heat. Such waste heat must be effectively removed to protect the electronic apparatus against failure. Various heat dissipation means are therefore developed to achieve effective removal of the heat generated by the IC chips.
One of the heat dissipation means is loop heat pipe (LHP). In a conventional loop heat pipe structure, there is included a reservoir or a compensation chamber for storing an adequate amount of working fluid, so that the evaporator for the loop heat pipe structure can be properly furnished with the working fluid and adapt to the volume change of the working fluid caused by density change thereof. The reservoir or compensation chamber also filters gas or bubbles in the working fluid, so that the working fluid is not interfered and damaged by the contained gas or bubbles.
While the conventional loop heat pipe structure provides a lot of advantages, it has a cylindrical evaporator that occupies a relatively large space and fails to directly contact with the heat source due to the round outer surface thereof. To overcome such disadvantages, a flat plate loop heat pipe (FPLHP) structure has been developed. In the currently available flat plate loop heat pipe structure, the compensation chamber is located above a wick structure provided inside the evaporator. The loop heat pipe structure with the compensation chamber provided above the wick structure in the evaporator tends to have serious heat leak, which brings difficulty in the start-up of the flat plate loop heat pipe structure and leads to increased total thermal resistance.
Moreover, the currently available flat plate loop heat pipe structure usually has an evaporator made of only one type of material for both of its wall portions and bottom. However, the bottom of the evaporator in contact with the heat source should have higher thermal conductivity than the wall portions of the evaporation. Further, due to the special construction of the flat plate loop heat pipe structure, when the bottom of the evaporator is in contact with the heat source, the heat is also transferred via the wall portions of the evaporator to heat the working fluid in the reservoir or compensation chamber. In some cases, the amount of heat transferred to the reservoir or compensation chamber is even equal to that causing the heat leak via the wick structure in the evaporator. A combined effect of the above two conditions badly affects the thermal performance of the flat plate loop heat pipe structure to even offset the advantages thereof.
Furthermore, the currently available electronic devices are so designed that they have constantly reduced size, volume and weight, and accordingly, largely reduced internal space. As a result, it has become the most important task to design a heat dissipation device that has small size and low profile to adapt to the limited inner space of the current electronic devices.